.Returns() with multiple return values does not work correctly the first time it's called

[chitoiur]

public interface IFoo
{
  int Read(int i);
}

[TestClass]
public class UnitTest1
{
  [TestMethod]
  public void TestMethod1()
  {
    var foo = Substitute.For<IFoo>();

    foo.Read(Arg.Is<int>(x => x == 0)).Returns(0, 1, 2);
    foo.Read(Arg.Is<int>(x => x == 1)).Returns(3, 4, 5);

    Assert.AreEqual(0, foo.Read(0));
    Assert.AreEqual(3, foo.Read(1));
    Assert.AreEqual(1, foo.Read(0));
    Assert.AreEqual(4, foo.Read(1));
    Assert.AreEqual(2, foo.Read(0));
    Assert.AreEqual(5, foo.Read(1));
  }
}

The problem is that the first Assert incorrectly fails, because the first call to Read(0) returns 1, instead of 0. I can reproduce this consistently and this is the most concise reproducer I could come up with.

[dtchepak]

Thanks for this.

The problem is that the second stub foo.Read(Arg.Is<int>(x => x == 1)) will actually call foo.Read(0) and cause the first of 0, 1, 2 to be returned. (I think it would work correctly if the conditions where ==1 and ==2 as it would filter out the 0 case.)

You could try working around the issue by specifying the ==1 case first:

[TestMethod]
  public void TestMethod1()
  {
    var foo = Substitute.For<IFoo>();
    foo.Read(Arg.Is<int>(x => x == 1)).Returns(3, 4, 5);
    foo.Read(Arg.Is<int>(x => x == 0)).Returns(0, 1, 2);
   ...

Fix notes
There is an issue with fixing this: currently the record call route returns the configured result so we can chain calls. So fixing this would break that behaviour. One option would be to not return the configured result for value types.

[chitoiur]

Thanks, confirming that the workaround is working. Specifically the workaround where I don't use x == 0, but instead start at 1.